Centrifugal pump



E. M. DETERS CENTRIFUGAL PUMP Jan. -7, 1964 Filed se t'. 20, 1960 2 Sheets-Sheet 1 ,E h u w Jan. 7, 1964 E. M. DETERS CENTRIFUGAL PUMP 2 Sheets-Sheet 2 Filed Sept. 20, 1960 4 5 o a u `u u 3 3 3 22 8 5 u I United States Patert Chee %696% 3,116,696 CENUGAL PUNE Elmer M, Detet-s, Davenport, lowa, assignor to Red Jiaclret Manatactnring Co., Davenport, Iowa, a corporatinaa of lowa Filed Sept. 20, 1960, Ser. No. 57,198 13 Clairns. (CE. 103-102) This invention relates to improvements in centrifugal pnnps and particularly to multi-stage centrifugal pumps.

In a cer 'riugal purnp having a single suction impeller, that is an impeller having an inlet only at one side, the impeller is snbjected to two opposing forces. The smaller of these forces, hereinafter sometimes referred to as the momentum force, is due to the change in momentum of the fluid entering the impeller inlet and is in a direction to urge the irnpcller axially away from the inlet. The other force on the impeller, referred to as the pressure force, is due to the difference in the area at the front and back sides of the impeller which are sub-- jected to purnp discharge pressure. This pressure force urges each impeller aXially in a direction toward the impeller inlet. The momentum force is generally quite small as Compared to the pressure force so that there is a resnltant thrust unbalance on each impeller in a direction toward the inlet. En a multi-stage pump with all of the impellers facing the same direction, the total thrust is proportional to the number of pump stages. Moreover, since the momentum force and the pressure force on each impeller vari-es under different pump Operating conditions, the total hydraulic thrust of a multi-stage centrifugal punp changes during operation of the pump.

lt is the common practice in multi-stage pumps of the type escrihed to mcunt the impellers on the shaft in such a manner that the axial thrust on each impeller is transmitted to the shaft, and to provide a single thrust hearing for taking up the entire aXial thrust on the sh; When a large number of pump stages are used, the total aXial thrust on the shaft becomes quite high and requires a very large and expensive thrust hearing. Further, when all of the impeliers are connected to the main drive shaft to transmit the axial impeller thrust to the hatt, it is necessary to very accurately space the impellers 'elative to the respective pump di'iuser casing so that the nzpellers are not pressed axially against the respective difiuser casing. Commonly, the impellers are mounted on the shaft with the adjacent impeller hubs in abutting engagement to space the impellers relative to the difiuser casings. This arrangement requires accurate machining of the length of the impeller hubs to provide the proper spacing. In a high pressure multi-stage pump, it is further necessary that the hub be formed of a sufiiciently rigid material to withstand the axial pressure applied to the hab by the other pump stages. in many applications, this preclndes the use of plastics in the forming of the puznp impellers. Further, when all of the impellers are connected to the shaft to transmit the axial thrust of the impellers to the shaft, it is necessary to provide adequate radial bearings to maintain the shaft in alignment with the thrust hearing. Thiis, it is frequently necessary to not only provide radial hearings at the ends of the shaft, but to also provide additional intermediate bearings every so may pump stages.

Pati'teol san. 7, tesa An important object of this invention is to provide a multi-stage centrifugal pump in which each impeller is hydraulically balanced so as to thereby avoid the necessity of providing a large thrust hearing for the pump shaft.

Another object of this invention is to provide a multistage centrifugal pump in which the impellers are mounted for free aXial float on the drive shaft and in which provi sion is made for increasing the pressure at the front side of the impeller over the pressure at the rear side thereof to counteract the normal unbalance on each impeller.

Yet another object of this invention is to provide a centrifugal purnp apparatus in accordance with the foregoing object in which the pressure at the front side of the impeller automatically increases and decreases to maintain substantial hydraulic balance of the irnpeller as the momentun and pressure forces on the impeller change under difi erent pump Operating conditions.

Still another object of this invention is to provide a centritugal pump having an improved arrangement for limting recirculation between the impeller hub and the drive shaft.

A further object of this invention is to provide a multistage centrifugal punp which can be economically manufactured and assembled and which has a high pump efciency.

These, together with various ancillary objects and ad vantages of this invention, will be more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in connection with the accompanying drawings wherein:

FIG. l is the longitudinal sectional view through a submersible motor pump unit embodying the present invention, the section through the pump being taken on a skewed plane through the flow passages of the pump impeller and diuser as indicated by the line 1-1 of FIG. 4;

FIG. 2 is an enlarged fragmentary sectional View through the nulti-stage centrifugal pump taken on the plane 2-2. of FIG. 3;

PKG. 3 is a transverse sectional View taken on the plane 3-3 of FIG. 2;

Piu. 4 is a transverse sectional View taken on the plane 4-4 of FIG. 2;

FEG. 5 is a transverse sectional View through the pump taken on the plane 5-5 of FG, 2;

FIG. 6 is a fragnentary view through the dififuser taken on the plane 6 6 of FIG. 3 and illustrating the diffuser transfer passages;

FIG. 7 is a bottom plan View of one part of the centritugal mpeller; and

PKG. 8 is a fragmentary exploded sectional view of the centrifugal impeller.

The improved centriugal pumping apparatus lil of the present invention is herein shown embodied in a submersble type pumping unit having a drive motor 11. In general, the pump apparatus includes a plurality of impellers 12 mounted on a drive shaft 13 and a pnmp casing 14 defining an impeller chamber for receiving each of the impellers and passages for transferring the fluid from the perphery of one centrifugal impeller to the inlet of the next adjacent impeller. Each of the impellers and pump casings for the several stages are iden tical in Construction and like numerals are utilized to designate corresponding parts in the several stages. The impellers 12 are of the type having a single inlet opening at one side of the impeller and, in accordance with the` present invention, are formed in two pieces to facilitatemolding of the impeilers, and which pieces are held together in the improved manner described hereinafter.. The impellers each include a hub 16 which is slidably' disposed on the drive shaft 13 and non-rotatably' keyed. thereto by one or more keys 15' which extend into keyways 13 in the drive shaft 13. For reasons set forth. hereinafter, the hubs 165 loosely surround the shaft 13- to permit limited radial fioat of the impelrers and, the: impel lers are disposed on the shaft with the adjaccnt ends` of the hubs axially spaced apart to pernit axial fioating: of the impellers relative to each other and to the shaft. 13. An impeller rear wall 13 is formed integrally with. the hub and extends outwardly therefrom. The impellers. also include a front wall 19 formed separate from the rear wall and impeller vanes 21 are formed on one of the walls to extend therebetween.

In the embodiment illus- `z llO trated, the impeller vanes 21 are formed integrally with,

the rear wall 18 of the impeller and spira l outwardly along an arc of progressively decreasing curvature from an inner end 21' spaced radially from the hub 16 to the outer end 21" located adiacent the periphery of the impeller. In accordance with the present invention, the front and rear walls of the impeller are connected together by means of bosses or pins 23 formed integrally with the bottom wall 19 and which extend into openings 24 in the impeller vanes 21. The pins 23 extend parallel to the axis of the impeller into the openings 24 to detachably interconnect the front and rear walls of the impeller and, as pointed out hereinafter, the front and rear walls are held in proper assembled relation by the fluid pressure conditions in the impeller and pump casing The front wall 19 of each impeller has an opening 26 therein around the hub 16 and a depending skirt 27' around the opening 26 to define the impeller inlet. The impellers are arranged on the shaft 13` with their inlets facing in the same direction.

The pump casing M of the present invention comprises a plurality of individual diffuser housings which are stacked together and enclosed in an outer sleeve 31 (PKG. l). The diffuser housings each include a periphera l wall 32, a thrust wall 33 and a diffuser wall 34 which define an impeller chanber 35 therebetween. The diffuser wall 34' is advantageously formed integrally with the peripheral wall 32 and the diffuser wall has an upstanding sleeve *36 at its inner end. The diffuser wall 34 has ramp portions 38, herein shown five in number (FIG. 3), disposed around its outer periphery' with the leading edge 38' of each ramp portion disposed adjacent the underside of the ditfuser plate and the trailing edge 38" spaced above the diffuser plate and from the leading edge of the next adjacent ramp portion so as to define annular transfer passages for transferring fluid from the periphery of the impeller chambers 35 to the upper side of the next adjacent diuser plate 34. The diffuser plate also has a plurality of diffuser vanes 41 formed on the upper surface thereof. The difuser vanes merge at their outer ends with the outlet end 33" of the ramp portions 38 and extend inwardly along an arcuate path of progressively increasing curvature to terminate at their inner ends 41' at a point spaced from the sleeve 36.

The thrust plate 33 is formed separate from the peripheral wall 32 and diffuser plate 34, in order to facilitate molding of the several parts. The thrust plate 33 of one stage is positioned to ovenlie the diffuser vanes 41 on the stage therebelow to partially enclose the diffuser passageways. In order to facilitate assembly of the several parts of the diffuser housings and stacking of the diffuser housings upon each other, the peripheral walls 32 are formed with an internal rabbet at their upper ends which defines an upwardly facing shoulder 43 disposed substantially co-planar with the upper edges of the diffuser vanes 41 and the thrust plate 33 of the next succeeding stage is supported on the shoulder 43. The axial depth of the rabbet in the upper end of each peripheral wall 32 is made grcater than the thiclness of the thrust plate 33 and the lower end of each peripheral wall is formed with an external rabbet or groove which defines a locating fiange 45 at the lower end of each peripheral wall which is adapted to be received in the internal rabbet of the diffuser housing thercbelow to radially locate the several diffuser housings on each other. As shown in PlG. 1, the assemhly of the stacled diffuser housings is disposcd within the sleeve 31 and an upper discharge member 4-3 and a lower motor mounting member 49 are threaded into opposite ends of the sleeve 31 and engage opposite ends of the stacked difuser housings to retain the same in asscmbled relation in the sleeve.

As will be noted, the area of the front wall 19 of the impeller is substantially less than the area of the rear wall 13 thereof, by reason of the provision of the inlet opening 26 in the front wall of the impeller. Since the front end rear walls of the impeller are exposed to a relatively high pressure in the impeller charnber 35 and *the inlet opening is subjected to a relatively lower inlct pressure, there is a pressure force or hydraulic thrust on each impeller which urges it in a direction axially toward the inlet, and which thrust increases as the pump output is throttled and decreases when the pump discharge is wide open. There is additionally an opposing momentum force on each impeller due to the change in momentum of the fiuid enter-ing the impeller inlet. This momentum force, however, is generally small as Cornpared to the pressure force so that there is a resultant force on each impeller, urging the same toward the inlet.

- This momentum force also changes under different pnmp Operating conditions and is a maximum when the pump discharge is wide open and a minimum when pump discharge is shut off. As previously noted, the impellcrs are slidably' and non-rotatably connected to the drive shaft 13 with the impeller hubs 16 axially spaced apart so as to permit free fioating of the impellers on the drive shaft and, in accordance with the present invention, provision is made for hydraulically balancing each individual impeller in such a manner that each impeller eifectively fioats within the impeller chamber during operation of the pump. Each thrust plate 33 has a central opening therein and an upstanding boss 51 around the opening, which boss defines a radially extending seal face 51' at the `upper side thereof and an axially extending seal face 51" around the opening. The flange 27 on the impellers 12 extends into the opening in the thrust plate with the outer periphery of the flange disposed relatively close to the annular seal face 51" to limit recirculation of liquid from the purnping chamber back to the impeller inlet. The radial clearance between the impeller flange 27 and the seal face 51" of the thrust plate has been exaggerated in FIG. 2 for purposes of illustration and in practice is preferabbiy of the order of .005 to .010 inch on a 4 inch pump. The impellers also have an annular face 53 at the under-side thereof adapted to cooperate with the radial seal face 51' on the thrust plate to provide a radial type seal face for limiting recirculation. When the pump is idle, the impellers rest on the boss 51 on the thrust plate and are supported thereby. It is contemplated that the impellers and the diffuser housing be formed of plastic and, in the pre-ferred form, a disc 53 of stainless steel or the like is interposed between the boss 51 and the underside of the impeller to prevent plastic to plastic rubbing contact therebetween. However, as pointed out hereinafter, provision is made for counter-balancing the hydraulic thrust on the impeller in such a manner that the impeller fioats axially away from the boss 51 on the thrust plate, when the pump is Operating in the normal range of pump Operating pressure, so that there is no rubbing contact between two surfaces having a high axial pressure therebetween.

In accordance with the present invention, a plurality of vanes 56 are provided on the side of the thrust plate 33 adjacent the front -wall 19 of the impellers for retarding rotation of the fluid at the front side of the impellers and thereby increasing the pressure at the front side of the impellers over the pressure in the respective impeller chamber at the rear side thereof. The vanes 56, as best shown in FIG. 5, extend from a point adjacent the outer periphery of the thrust plates inwardly in an arc of progressively increasing curvature to the central boss 51 or the respective thrust plate. The vanes are spiralled or skewed in the direction of rotation of the impellers so as to force fiuid from a point adjacent to the periphery of the impeller chamber 35 inwardly towards the axis and to retard rotation of this fluid. This increase in pressure at the front wall 19` of the irnpellers counteracts the normal axial thrust on the impellers due to the presence of the inlet opening at the front side thereof and, when the pressure at the front side of the impellers increases sufficiently, the impellers are moved axially away from the thrust plate. As the impellers move away from the thrust plate, the vanes 56 become less effective to retard rotation of the fluid at the underside of the impeller and, in addition, the clearance between the radial seai face 51' on the thrust plate and the corresponding seal face 53` on the impeller is increased so that there is a somewhat greater reciroulation of fluid back to the impeller inlet. The impellers will move away from the respective thrust plate until the pressure acting on the front Wall of the impeller is sufficient to overcome the relatively lower pressure in the impeller chamber acting on the larger area of the rear wall of the impeller. The impel ler will then axially float in the impeller chamber at the point where the opposing pressures acting thereon are balanced. When the pump is Operating at the wide open position of its characteristic curve, the momentum force increases and the pressure force decreases. Under these conditions, the impellers will therefore progressively move further away from the thrust plates to reduce the efficiency of the ribs or vanes 56 and to increase the leakage path between the radial seal faces 51 and 53. Advantageously, a thin disc or Washer 58 may be interposed between the rear wall 18 of each impeller and the difuser wall 34 to prevent plastic to plastic rubbing contact under abnormal Operating conditions in which the thrust un aiance on the impeller is in a direction to urge it away from the inlet opening of the impeller.

When the pump is in operation, the pressure in the impeller passages is somewhat below the pressure in the surrounding impeller charnber, due to the slowing down of the fluid in the impeller chamber so that there is a pressure unbalance on the opposite walls of the impellers which tends to hold the same in assembled reiation. This pressure unbalance is augmented by the vanes 56 which, as previously described, increased the pressure at the front wall of the impeller above the pressure at the rear wall thereof. However, in order to prevent accidental disassenbly of the front and rear walls of the impeller, when the pump is not Operating, or under abnormal operatin conditions, the pins 2.3 and opening 24- ir the impellers are made axially longer than the spacing between impellers and the adjacent walls 33 and 34 of the ditt-user housing. Consequently, when the impellers are assembled in the diffuser housings, the impeller sections can not axially separate a distance sufiicient to prevent complete withdrawa-l of the pins 23` from the opening 24. As soon as the pump is put into operation, the pressure conditions in the impeller chambers urge the sections of the impellers into close engagement.

It will thus be apparent that recirculation between the impeller charnber and the inlet opening is controlled both bythe radial seal face 51' and by the axial seal face 51" on the thrust plate. e pump is preferably designed so that when the pump delivers its nominal capacity and up until the pump discharge pressure reaches the shutof or maximum output of the pump, the impeller extends olosely adjacent to or even rubs lightly against the radial seal face 51' on the thrust plate. Thus, the radial seal face functions to control recirculation in that portion of the pump performance curve between nominal Capacity and shut-off pressure so as to improve the performance and efficiency of the pump near shut-off pressure. However, when the pump discharge is wide open, the pump impellers tend to move upward due to the momentum of the fi-uid entering the impeller inlets and the reduced pressure in the impeller chambers 35. Under these conditions, the axial seal face 51" and the cooperating flange 27 on the impeller are re lied upon to limit recirculation from the impeller chamhers back to the pump inlets.

In order to control recireulation between the diffuser housings and the impeller hubs, the letter are fornied with upper and lower axial extensions 16' and 16". The upper axial extensions extend into the lower portion of the sleeve 36 on the ree ective diffuser plate 34 and the lower axial extensions project into the upper end of the sleeves 36 on the stage therehelow. he hub extensions provide a close running flt with the sleeves on the diffuser housing so that -the hubs are effeotively radiaily supported by these sleeves, sufcient clearance being provided between the h ub and the drive shajt 13 to permit the hubs to become aligned with the sleeves. 'In the 4 inch pump illustrated, the clearance between the iinpeller hubs ?to and the sleeves 36 is preferably of the order of .GGS to .010 to control reeiroulation therebetween. Recirculation between the hubs and the drive shaft is controled by an inwardly projecting tapered lip of; provided on the upper end of each of the hubs, and which lip extends around the periphery of the hubs and is stepped in ac cordance with the splined opening in the hub to form a wiping seal with the shaft. As will be noted from FIG. 2, the lip 61 is tapered upwardy and, when the impellers are assembled onto the shaft, the iip is inclined upwardly in the direction toward the high pressure zone. Consequently, the pressure on the lip tends :to press more firmly into close rubbing fit with the drive shaft ET).

The motor 11 for driving the shaft ray be of any conventional constnuction and, as shown herein, includes a stator '71 having windings 72, which stator is disposed in an outer sleeve '73. An inner sleeve 74 extends through the st-ator bore and is sealed at opposite ends by rings 75 to the outer shell. A rotor ?e is mounted on a shaft 77, which shaft is rotatabiy supported by bearings 73 .and 79 in upper and lower end belle 31 and 3?. attached to the outer shell. A shaft seal is provided at the upper end of the shaft and an expansihle chamber 84 is mounted in the lower end bell for equal izing the pressures between the interior and the exterior of the motor. The connectinzg member 49 is attached to the upper end bell 81 of the motor to suspend the moto-r froni the pump and the motor shaft '77 is connected to the pump shaft 13 by a coupling 86.

Since the pump impellers are free to hoat axially on the drive shaft 13, there is no thrust transmitted from the impellers to the shaft and it is therefore not necessary to provide a large thrust hearing for the pump shaf't. Relatively small thrust bearings '33 and flit are provided in the motor housing for limit-ing axial thrust on the motor rotor 76, which thrust bearings need only be large enough to take the end thrust on the rotor.

From the foregoing it is thought that the Construction operation of the improved pumping apparatus will be readi-ly understood. The vanes 56 on the thrust plate retard rotation of the fluid at the front side of the impellers to increase the pressure thereat. The impellers are free to `axially float in the impeller chambers and move away from the vanes a distance such that the axial iydr-aulic thrust on the impellers Will be balanccd. This provides a self-regulating type of hydraulic balance for the impellers. Since the impellers do not exert a large axial th'ust on the shaft ES), it is unncessary to provide a large thrust hearing for the pump drive shaft and wear on the impellers and ditfuser housings is substantially avoided. Assembly of the impellers and difuser housings of the pump is also markedly facilitated by the present Construction. The front and rear walls of the impellers are molded in separate pieces for ease of molding, and are held together by the pressure conditions in the imeller chambers so as to eliminrte the necessity of a separate assembly step to rigidly secure the impeller sections together. The bosses 23 and openings 24 which interconnect the impeller sections are, moreover, designed so as to prevent accidental detachment of the impeller sections when the pump is not operatin or when the pump is Operating under abnormal pressure conditions. In addition, the resilient sealing lips 61 on the hubs enable Construction of the hubs so as to pcrrnit limited radial fiosting of the impeller hubs on the drive shaft, so that the hubs can align themselves with the sleeves 36 of the ditfusers.

I claim:

l. A multi-stage diffuser type pump ccrnprising, a drive shaft, a plurality of pump impellers each having a hub means sldably and non-rotatably mounting said hubs on the shaft with the hubs axially spaced apart for free axial iloat of the impellers on the shaft, each impeller having front and rear walls defining a central inlet opening in the front wall and impeller passages extending from the inlet opening toward the outer periphery of the impeller, said impellers being disposed on the shaft with the inlet openings facing in the same direction, a pump housing comprising a plurality of stacked impeller casings one for each impeller, said impeller casings each defining an impeller chamber and including a peripheral wall surrounding each impeller; a th' ust wall extending inwardly from the perpheral wall and spaced fl'Ofil the front side of a respective impeller; and a diffuser Wall extendiug inwardly from the peripheral wall and spaced axially from the rear Wall of the respective impeller; said thr ust wall having a central opening therein, each impeller and the respective thrust wall having telescoping seal means thereon around said inlet opening in the impeller for limitin-g recirculaticn from the impeller chamber back to the impeller inlet, said diffuser walls each having a central opening therein and `an elongated sleeve around said openings, said impeller hubs having a first hub extension thereon extending from the rear wall into the sleeve on the respective difiuser wall and a second hub extension thereon extending into the sleeve on the diffuser wall of the preceding stage for radial support thereby, said casings each defining difuser passages for conveying liquid from the periphery of each impeller chamber to the inlet of the impeller in the next succeeding stage, and ribs on said thrust wall projecting toward said front wall of the impeller and extending from the outer periphery of the impeller chamber toward the inlet opening of the impeller for retarding rotation of the fiuid at the front side of the impeller whereby to in crease the pressure at said :front =wall above the pressure at said rear Wall of the impeller when the pump is in operation.

2. The combination of claim 1 wherein said impeller hubs are formed of tresilient plastic and loosely receive said shaft, said hubs having an integral resilient flange on the end of said first extension, said fiange extending inwardly into Wiping engagenent with said shaft for limiting reciroulation between the hulb and shaft.

3. A centrifugal pump comprising a drive shaft, an impeller mounted `on said drive `'shaft and having front and rear walls `defining a lcentral inlet opening in the front wall and vanes on one of said walls` forming impeller passages between said front and rear walls extending from said inlet opening to the periphery of the impeller, casing means surrounding said impeller and having walls spaced rfrom the front and rear walls of the impeller to define an impeller chamber therebetween, characterizecl in that said front and rear walls of the impeller are formed separate from each other and have a plurality of annularly spaced interfitting bosses and sockets thereon nonrotating connecting said front and rear walls while permitting free axial movement of the front and rear walls relative to each other, and means in said casing means for increasing the pressure on said front wall above the pressure at the outer ends of said impeller passage during operation of said pump to normally maintain said front and rear walls of the impeller against axial separation.

4. A 'centrifugal pump comprising a drive shaft, an impeller mounted on said drive shaft and having front and rear walls defining a central nilet opening in the front wall, vanes on `one of said walls defining impeller passages between said front and rear walls extending from said inlet opening to the periphery of the impeller, a diffuser casing surrounding said impeller and having front and rear walls respeetively space d from the front and rear walls of the impeller, said vanes having openings extending thereinto parallel to the axis of the impellers, the other of said walls of the impeller having integral pins thereon sldably extending into said openings in the vanes and non-rotatably connecting the front and rear walls of the impeller while permitting free relative axial movement therebetween, said front and rear walls of the impeller being held against axial separation solely by the fluid pressure in said diffuser casing acting on' said front and rear walls.

5. A multi-stage centrifugal pump comprising a drive shaft, a plurality of impellers each having a hub, means non-rotatably mounting said hubs on said drive shaft, said impellers each having a rear 'wall extending outwardly from the hub and a front 'wall defining a central inlet opening around the hub, said impellers also including vanes on one of said walls defining impeller passages between the front and rear walls extending from said inlet opening -to the periphery of the impeller, a diffuser casing surrounding each impeller and having front and rear walls respectively Sp aced from the front and rear walls of the impeller, said vanes having openin gs extending thereinto parallel to the axis of the impeller and pins on the other of said impeller walls sldably extending into said openings in the vanes to non-rotatably connect said front and rear walls of the impeller while permitting free relative axial movement therebetween, said front and rear walls of the impeller being held against axial separation solely by the fluid pressure in said diffuser casing actin g on said front and rear walls.

6. The combination of claim 5 wherein said impellers are formed of plastic and have an integral tapered ange on one end of the hlllb extending inwardly into wiping contact with said shaft to limit recirculation of fluid between the hubs and the shaft.

7. A Inu1ti-stage diuser type 'centrifugal pump for pumping fluid from a main pump inlet to a main pump outlet comprising, a drive shaft, a plurality of pump inipellers each having a central inlet opening; a front wall extending outwardly from the central inlet opening; a hub; a rear wall extending outwardly from the hub; and impeller passages extending between the front and rear walls from the central inlet opening toward the outer periphery of the impeller, means sldably and non-rotatably mo unting said hubs on the shaft with the hubs axially spaced apar t for free axial fioat of the impellers on the shaft, said impellers being disposed on the shaft with the inlet openings facing in the same direction, a pump casing surrounding said impellers and including a plurality of thrust walls each spaced axially from the front wall of a respective impeller and a pluralty of diffuser walls each spaced axially from the rear wall of a respective impeller to define a plurality of impeller chambers, said pump cusing including means dening `a plurality of diffuser pas- &116398 sages for trahsferring liquid from the periphery of each impeller chanber to the rear side of the respective ditfuser wall and into the inlet opening of the impel-ler of the next adjacent pump stage, -the difference between the fluid pressures actng on the rear wall of each impeller and the fluid pressure at the inlet opening of the impeller producng an axial hydraulic thrust on each impeller in a direction toward the inlet opening and which hydraulic thrust is a maximum when the flow through the purnp outlet is shut off and which hydraulic thrust ide'creases as the flow from the pump outlet is a'ircrealsed, and a plu'ality of ribs on each thrust wall at the side .there o f adjacent the front of the respective inpeller for retarding rotation of the fluid at the front wall of the impeller to thereby produce a counteracting pressune at said front wall of each impeller which is su bstantially greater than the pressure at the rear wall of that impeller when the front wall of the impeller is disposed closely adjacent the ribs and which counteracting pressure decreases as the impeller moves axially away from the ribs, said irnpellers being s'o dimensioned in relation to said impeller charnbers to perm it limited independent floet of *the impellers axia lly within their respective charmberr and along the shaft whereby the impellers can Shift axially away from the ribs to decrease the counteracting pressure at the front wall of the impellers as said hydraulic thi-List decreases.

8. A multi-stage difuser type centrifugal pump for pumpng fluid from a main pump inlet to a main pump outlet conprsing, a drive shaft, a plnrality of pump impellers each having a central inlet opening; a front wall extending outwardly from the central inlet opening; a hub; a rear wall extending outwardly from the hub; and impeller passages extending between the front and rear walls from the central inlet opening toward the outer periphery of the impeller, means slidably and non-rotatably mountng said hubs on the shaft with the hubs axially spaced apart for free axial float of the impellers on the shaft, said impellers being disposed on the shaft with the inlet openings facing in the same direction, a punip casing surrounding said impeilers and including a plurality of thrust walls each spaced axially from the front Wall of a respective impeller and a plurality of difluser walls each spaced axialiy from the rear wall of a respective impeller to define a plurality of impeller chambers, said punip casing including means defining a plurality of difuser passages for transferring liquid from the periphery of each impeller chamber to the rear side of the respective difiuser wali and into the inlet opening of the impeller of the next a jacent pump stage, the difference between the fluid pressures acting on the rear wall of each impeller and the fluid pressure at the inlet opening of the impeller producing an aXial hydrauiic thrust on each impeller in a direction toward the inlet opening and which hydraulic thrust is a maximum when the flow through the pump outlet is shut oli and which hydraulic thrust decreases as the flow from the pump outlet is increased, and a plurality of ribs on each thrust wall at the side thereof adjacent the front of the respective impeller for retarding rotation of the fluid at the front wall of the impeller to thereby produce a counteracting pressure at said front Wall of each impelier which is substantially greater than the pressure at the rear Wall of that impeller when the front Wall of the impeller is disposed closely adacent the ribs and which counteracting pressure decreases as the impeller moves axially away from the ribs, said impellers being so dimensioned in relation to said impeller chambers to permit limited independent float of the impellers axially within their respective chamber and along the shaf't Whereby the impellers can Shift axialiy away from the ribs to decrease the counteracing pressure at the front wall of the impellers as said hydraulic thrust decreases, each impeller and thrust wail having telescoping axially extending seal faces around said inlet openings in said impellers for limiting recircniation to said impeller inlet as the impellers Shift axially away from their respective thrust wall.

9. The combination of claim 8 wherein said ribs have an entrance end adjacent the periphery of the respective impeller and curve inwardly in the direction of rotation of the impeller toward said seal faces.

10. The combination of claim 8 wherein said hubs are each loosely disposed on said shaft and have a resilient inwardly extending peripheral flange thereon disposed in wiping engagement with said shaft for limiting recirculation of fluid between the hubs and shaft.

11. The cornbination of claim 8 wherein said impellers are formed of a resilient plastic material and have an integral inwardiy extending flange on the hubs at the end thereof rernote froni the impeller inlet opening, which flange is disposed in wiping engagement with said shaft for limitng recirculation of fluid between the -hu'bs and the shaft.

i2. The combination of claim 8 wherein said front and rear walla of said impeller are formed of two separate pieces, one of said walls having a plurality of annularly spaced openings extending thereinto parallel to the axis of the impelier and the other of said walls having bosses slidabiy extending into said annularly spaced openings to non-rotatably connect said front and rear Walls whereby said front and rear walls are free to axially separate, said front and rear walis being held against axial separation during operation of the pump solely by the fluid pressure acting on said front and rear walls of the impeller.

3. A triniti-stage diffuser type centrfugal pump for pumping fluid from a main pump inlet to a main pump outlet comprising, a drive shaft, a plurality of pump impeilers each having a central inlet opening; a front wall extending outwardly from the central inlet opening; a hub; a rear Waii extending outwardly from the hub; and impeller passages extending between the front and rear walis from the central inlet opening toward the outer periphery of the iinpeller, means sldably and non-rotatably mounting said hubs on the shaft with the hubs axially spacel apart for free axial oat of the impellers on the shaft, said impellers being disposed on the shaft with the inlet openings facing in the same direction, a pump casing surrounding said impellers and including a plurality of thrust walls each spaced axialiy from the front wall of a respective impeiler and a plurality of diffuser walls each spaced axially from the rear wall of a respective impeller to dene a plurality of impeller chambers, said pump casing including means dening a plurality of diffuser passages for transferring liqnid from the periphery of each impeller chanber to the rear side of the respective diifuser wail and into the inlet opening of the rnpeller of next adjacent pump stage, the difference between the fluid pressures acting on the rear wall of each impeller and the fluid pressure at the inlet opening of the impeiler producing an axial hydraulic thrust on each impeller in a direction toward the inlet opening and which hydraulic thrust is a maximum when the flow through the pump outlet is shut off and which hydranlic thrust decreases as the flow from the pump outlet is increased, and a plurality of ribs on each thrust wall at the side thereof adjacent the front of the respective impeller for retarding rotation of the fluid at the front wall of the impeller to thereby produce a counteractng pressure at said front wail of each impelier which is substantiaily greater than the pressure at the rear wall of that impeller when the front wall of the impeller is disposed closely adjacent the ribs and which counteracting pressure decreases as the imr moves axially away from the ribs, said impellers being so dmensioned in reiation to said impeiler chambers to permit limited independent float of the impellers axiaiiy within their respective chamber and along the shaft where by the impellers can Shift axially away from the ribs to decrease the counteracting pressure at the front wall of the impeilers as said hydraulic thrust decreases, said thrust walls each having a central opening therein and an annular rim around said central opening at the side adjacent the front wail of the impeller and deflning a radially eX- tending seal face and nn axially extending sea! face around said central opening, said impellers each having a radial seal face on the front Wall thereof engageable with the radial seul face on the respective thrust wall and a flange extending around the inlet opening in impellers and tele- 5 scopically received in said axially extending seal face on the respective thrust Wall to limit recirculation to said imeler inlet as the impellers Shift axially away from the respective thrust wall.

References Cte n the file of ths patent UNITED STATES PATENTS 1,()90/G73 1,271,072 2,361,521 2,630,343 2,753,807 2,854,926 2,882,C77 2327536 2,954,739 &0253300 3,070,026

Kieser Mar. 10, 1914 Parsons July 2, 1918 Yates Oct. 31, 1944 Jones et al Mar. 3, 1953 Lung July 10, 1956 Haight et al. Oct. 7, 1953 Marsh Apr. 14, 1959 Rhoades Mar. 8, 1960 Lung Oct. 4, 1960 Welle et al Mar. 20, 1962 Lung Dec. 25, 1962 FOREIGN PATENTS Germany July 15, 1914 Great Britain Nov. 19, 1925 

1. A MULTI-STAGE DIFFUSER TYPE PUMP COMPRISING, A DRIVE SHAFT, A PLURALITY OF PUMP IMPELLERS EACH HAVING A HUB MEANS SLIDABLY AND NON-ROTATABLY MOUNTING SAID HUBS ON THE SHAFT WITH THE HUBS AXIALLY SPACED APART FOR FREE AXIAL FLOAT OF THE IMPELLERS ON THE SHAFT, EACH IMPELLER HAVING FRONT AND REAR WALLS DEFINING A CENTRAL INLET OPENING IN THE FRONT WALL AND IMPELLER PASSAGES EXTENDING FROM THE INLET OPENING TOWARD THE OUTER PERIPHERY OF THE IMPELLER, SAID IMPELLERS BEING DISPOSED ON THE SHAFT WITH THE INLET OPENINGS FACING IN THE SAME DIRECTION, A PUMP HOUSING COMPRISING A PLURALITY OF STACKED IMPELLER CASINGS ONE FOR EACH IMPELLER, SAID IMPELLER CASINGS EACH DEFINING AN IMPELLER CHAMBER AND INCLUDING A PERIPHERAL WALL SURROUNDING EACH IMPELLER; A THRUST WALL EXTENDING INWARDLY FROM THE PERIPHERAL WALL AND SPACED FROM THE FRONT SIDE OF A RESPECTIVE IMPELLER; AND A DIFFUSER WALL EXTENDING INWARDLY FROM THE PERIPHERAL WALL AND SPACED AXIALLY FROM THE REAR WALL OF THE RESPECTIVE IMPELLER; SAID THRUST WALL HAVING A CENTRAL OPENING THEREIN, EACH IMPELLER AND THE RESPECTIVE THRUST WALL HAVING TELESCOPING SEAL MEANS THEREON AROUND SAID INLET OPENING IN THE IMPELLER FOR LIMITING RECIRCULATION FROM THE IMPELLER CHAMBER BACK TO THE IMPELLER INLET, SAID DIFFUSER WALLS EACH HAVING A CENTRAL OPENING THEREIN AND AN ELONGATED SLEEVE AROUND SAID OPENINGS, SAID IMPELLER HUBS HAVING A FIRST HUB EXTENSION THEREON EXTENDING FROM THE REAR WALL INTO THE SLEEVE ON THE RESPECTIVE DIFFUSER WALL AND A SECOND HUB EXTENSION THEREON EXTENDING INTO THE SLEEVE ON THE DIFFUSER WALL OF THE PRECEDING STAGE FOR RADIAL SUPPORT THEREBY, SAID CASINGS EACH DEFINING DIFFUSER PASSAGES FOR CONVEYING LIQUID FROM THE PERIPHERY OF EACH IMPELLER CHAMBER TO THE INLET OF THE IMPELLER IN THE NEXT SUCCEEDING STAGE, AND RIBS ON SAID THRUST WALL PROJECTING TOWARD SAID FRONT WALL OF THE IMPELLER AND EXTENDING FROM THE OUTER PERIPHERY OF THE IMPELLER CHAMBER TOWARD THE INLET OPENING OF THE IMPELLER FOR RETARDING ROTATION OF THE FLUID AT THE FRONT SIDE OF THE IMPELLER WHEREBY TO INCREASE THE PRESSURE AT SAID FRONT WALL ABOVE THE PRESSURE AT SAID REAR WALL OF THE IMPELLER WHEN THE PUMP IS IN OPERATION. 